French patent of invention 2 506 726 in the name of the Applicant company discloses such a device, one of the containers being constituted by a flask having an externally threaded neck. The holding member is constituted by a ring inserted in the neck and bearing against the end wall thereof by means of an annular rim. The other container is constituted by a capsule screwed to the neck, including a central chimney on which the above-mentioned ring is pressed. The shutter comprises a plug closing the chimney during separate storage of the components, and connected to the ring by a bridge of hinge-forming material.
Sealing is provided between the flask and the capsule by the ring being compressed between the neck and the chimney.
Screwing the capsule onto the flask causes the plug to pivot and puts the capsule into communication with the flask. The bridge of hinge-forming material connecting the plug to the ring serves to prevent the plug from dropping to the bottom of the flask.
The ring must be pressed hard against the chimney and the neck in order to achieve the required degree of sealing, thereby impeding the screwing movement of the capsule to a considerable extent, so that the known device is not easy to use.